Oak, the architecture of Apache Jackrabbit 3
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Apache Jackrabbit is just about to reach the 3.0 milestone based on a new architecture called Oak. Based on concepts like eventual consistency and multi-version concurrency control, and borrowing ideas from distributed version control systems and cloud-scale databases, the Oak architecture is a major leap ahead for Jackrabbit. This presentation describes the Oak architecture and shows what it means for the scalability and performance of modern content applications. Changes to existing Jackrabbit functionality are described and the migration process is explained.
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Oak, the architecture of Apache Jackrabbit 3
- 1. Oak the architecture of Apache Jackrabbit 3
- 2. Subsection Title • Text • Text
- 3. Resources • http://jackrabbit.apache.org/oak/ • Docs • http://jackrabbit.apache.org/oak/docs/ • Code • https://svn.apache.org/repos/asf/jackrabbit/oak/trunk/ • https://github.com/apache/jackrabbit-oak • Builds • http://ci.apache.org/builders/oak-trunk/ • https://travis-ci.org/apache/jackrabbit-oak
- 4. Outline • Tree model • Updating the tree • Refresh and garbage collection • Concurrency and conflicts • Interlude: Implementations • Replicas and sharding • Access control • Comparing revisions • Commit hooks • Observers • Search • Big picture
- 5. Tree model
- 6. a d b c Paths as identifiers / /a /a/b /a/c /d
- 7. a d b c Paths as identifiers / /a /a/b /a/c /d
- 9. ?
- 10. r1 r2 HEAD r1: /d r2: /d r1: /a/c r2: /a/c
- 11. Refresh and garbage collection
- 12. refresh
- 13. garbage
- 16. r1 r2br2a
- 18. Conflict handling strategies a. Fully serialized commits • fail on conflict, no concurrent updates b. Partially serialized commits • fail on conflict, concurrent conflict-free updates c. Partial merge logic • conflict markers, manual conflict resolution d. Full merge logic • conflicting changes may be lost
- 20. MicroKernel/NodeStore • Implementation of the tree/revision model Responsible for Clustering Sharding Caching Conflict handling etc. Not responsible for Type validation Access control Search Versioning etc.
- 21. Current implementations DocumentMK TarMK (SegmentMK) Persistence backends MongoDB, JDBC (WIP) Local FS (tar files) Conflict handling Partial serialization Full serialization Clustering MongoDB clustering Simple failover Sharding MongoDB sharding N/A Single-node performance Moderate High Key use cases Large deployments (>1TB), concurrent writes Small/medium deployments, mostly read
- 23. master copy full replica cache Replicas and caches
- 24. by path by level by hash Sharding strategies with caching
- 25. Access control
- 27. Existentialism • All (syntactically valid) paths can be traversed • But the identified node might not exist • For example: root.getChildNode(“a”).exists() -> false root.getChildNode(“a”).getChildNode(“b”).exists() -> true! • Implemented as a decorator over the MK
- 29. What changed?
- 30. Content diff • Tells what changed between two content trees • Cornerstone of most higher-level functionality • validation • indexing • observation • etc.
- 31. r1 r2b r2a r3 Examples r1 -> r3 “a” modified “b” removed “d” modified “e” added r1 -> r2a “a” modified “b” removed r1 -> r2b “d” modified “e” added
- 32. Commit hooks
- 33. If this changed, commit this instead
- 34. Commit hooks • Based on given before and after states, a hook can: • fail the commit, or • pass the commit unmodified, or • pass the commit with modifications • Key plugin mechanism in Oak • All configured hooks are applied in sequence • Used for much higher level functionality • Often implemented using a content diff
- 35. Examples • All kinds of validation • node types, access control, references, etc. • Trigger-like functionality • autocreated content, default values, etc. • In-content index updates • etc.
- 36. Types of hooks CommitHook Editor Validator Content diff Optional Always Always Can modify commit Yes Yes No Programming model Simple Callbacks Callbacks Performance impact High Medium Low
- 37. Observers
- 38. Observers • Based on given before and after states, an observer can: • observe what changed in the content tree • Invoked after the commit, unlike commit hooks • Always asynchronous for changes from other cluster nodes • Depending on backend, can be synchronous for changes on the local cluster node • Often implemented using a content diff
- 39. Examples • JCR Observation • External index updates • Cache invalidation • Logging • etc.
- 40. Search
- 42. Query processing steps 1. Parsing a. Select matching parser b. Parse the query string 2. Execution a. Estimate cost per index b. Select index with the least cost estimate c. Execute the query against the index 3. Post-processing a. Filter results on access control and additional constraints b. Apply sorting, grouping, faceting, etc.
- 43. Index implementations • Property index • Reference index • Lucene index • in-content • local file system • Solr index • embedded • external
- 44. Big picture
- 45. MicroKernel Oak Core Oak JCR Oak API NodeStore API JCR API Plugins
- 46. Questions?